-- -- Others -- the world is watching reports. Of -- downed passenger jet did Russia and Ukraine border. And it looks like it may be a terrible tragedy. Right now we're working determine. Whether there were American citizens on board. That is our first priority and I've directed my national security to stay in close contact. With the Ukrainian government. The United States will offer any assistance we can't help determine what happened and why. And as a country are. Thoughts and prayers are with all the -- -- -- passengers wherever they call. Very brief comments from the president are right they are calling this a terrible tragedy. Trying to determine the United States is right now what happened and why also he's in the first priority. Whether American citizens. Were on board John -- the present so far very careful. Very careful. All about a shortage you could possibly be to talk about this saying that his top priority is determining whether or not there -- any. American citizens on board -- we've been in touch with officials here at the White House -- at the State Department. And they tell us right now no confirmation. Whether or not there were Americans on board and also on the president's saying that the US will of course be helping. -- that investigation and investigation that. Would be severely complicated by -- -- if in fact the black box has turned over to the Russian government and is not shared. But very short at the demonstrates exactly what you were talking about George which is. The president does not want to be in a position of of overreacting or or escalating he wants to. That -- but they're saying years let's get to the bottom of this before we jump to any. Conclusions let's thoroughly investigate. Let's do this in a measured. Way and not make any mistakes in the process.

This transcript has been automatically generated and may not be 100% accurate.

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